Danny Masterson strenuously denies old rape allegations against him ... and he's claiming Leah Remini played a part in the cases coming to light.

A rep for the "That '70s Show" star tells TMZ ... they're aware of 16-year-old allegations made by one of Danny's ex-girlfriends, and 2 other women. The ex went to police, and we've confirmed there is an open investigation. That investigation was the subject of a blog post accusing the Church of Scientology of covering up multiple rape claims.

Danny's calling BS and says Leah is just trying to boost ratings for her show, 'Scientology and the Aftermath.' Danny's rep claims Leah spoke to the ex-girlfriend, and after Leah's show aired ... the other 2 women contacted Leah too.

The rep goes on to say, "The alleged incident occurred in the middle of their 6 year relationship, after which she continued to be his longtime girlfriend."

Danny's rep also says the woman continued to pursue him after he ended the relationship.

He believes the case has no merit. We've reached out to Leah's camp, but nothing back yet.